The present invention relates to a novel rare earth metal-containing alloy for permanent magnets. More particularly, the invention relates to a rare earth metal-containing alloy for permanent magnets of which the rare earth metal constituent is composed of a combination of samarium and cerium as combined with cobalt as the main component of the transition metal constituent partially replaced with iron and copper.
In the prior art, there have widely been undertaken many investigations on the rare earth metal-containing alloys for permanent magnets of the type (Sm, Ce)(Co, Fe, Cu).sub.z as a modification obtained by partial substitution of cerium for samarium and iron and copper for cobalt in the prototypical alloys of SmCo.sub.z. See, for example, (a) IEEE Trans. Mag., volume Mag-10, page 313 (1974) and (b) Japan. Journal of Appl. Phys., volume 12, page 761 (1973). The highest value of the maximum energy product (BH).sub.max, which is the most representative parameter for the magnet performance, is 20.2 MGOe as is reported in the reference (b) above.
On the other hand, it is already known that, for the magnet alloys expressed by the formula Sm(Co, Fe, Cu).sub.z or Ce(Co, Fe, Cu).sub.z, addition of a transition metal such as titanium, zirconium, manganese, hafnium and the like is effective in increasing the coercive force of the magnet so that the content of the iron as well as the relative amounts of the non-rare earth metals to the rare earth metal as represented by the suffix z can be made larger contributing to the increase of the saturation magnetization. See, for example, (c) Japan. Journal of Appl. Phys., volume 17, page 1993 (1978) teaching the addition of titanium to a samarium-based magnet alloy; (d) IEEE Trans. Mag., volume Mag-13, Page 1317 (1977) teaching the addition of zirconium to a samarium-based magnet alloy; (e) Japanese Patent Publication 54-33213 issued 1979 teaching the addition of manganese to a samarium-based magnet alloy; and (f) Appl. Phys. Lett., volume 30, page 669 (1977) teaching the addition of titanium to a cerium-based magnet alloy.
Among the permanent magnet alloys disclosed in the above given references, those with samarium as the rare earth metal constituent are superior by far to the cerium-based ones in many of the magnetic characteristics. Unfortunately, samarium metal is very expensive in comparison with cerium metal so that there have been made several attempts to replace part of the samarium with less expensive cerium metal with an object to improve the magnetic properties of the magnet alloys containing the binary rare earth metal constituent of samarium and cerium by the admixture of any one of the transition metals of titanium, zirconium, manganese and the like as a partial replacement of the non-rare earth constituent of cobalt, iron and copper. See, for example, (g) Japanese Patent Publication 53-2127 issued 1978 teaching the addition of manganese to an alloy of the type (Sm, Ce)(Co, Cu).sub.z ; (h) Japanese Patent Publication 54-38973 issued 1979 teaching the addition of titanium to an alloy of the type (Sm, Ce) Co, Cu).sub.z ; and (i) Fourth Int. Workshop on RE.Co Permanent Magnets, page 387 (1979) teaching the addition of zirconium to an alloy of (Sm, Ce)(Co, Fe, Cu).sub.z. The highest value of the maximum energy product of the permanent magnets disclosed in these references cannot exceed 19.8 MGOe as is shown in the last given reference.
Accordingly, there has been eagerly desired to improve the magnetic properties of the alloys of the type (Sm, Ce)(Co, Fe, Cu).sub.z with respect to the coercive force and the squareness of the hysteresis loop with a consequent increase in the value of the maximum energy product even with less strictly defined consitions for the thermal treatments including sintering and aging.